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White Foam

Billowing, crisp white foam, often during startup or low MLSS.

1Symptom

Billowing white foam, often light and crisp, on the aeration basin. Common during startup, after a washout, or when MLSS is low and SRT short. Can also come from detergents or toxic upset.

2Check first

  1. Check MLSS and SRT.
  2. Check for recent washout or toxic events.
  3. Look at the foam: detergent foam is white and crisp; filament foam is brown.

3Possible causes

  • Young sludge (low SRT, high F/M) with protein and surfactants not yet degraded.
  • Surfactant loads.
  • Toxic upset that killed biomass.

4Next investigation

  • Calculate SRT and F/M.
  • Review influent sources for surfactants.

5Corrective actions

  1. Reduce wasting to build MLSS and SRT.
  2. Use water sprays to break foam.
  3. Investigate surfactant sources.

6When to call for help

  • Foam appears with a sudden loss of treatment (possible toxicity).
Make one change at a time, record it, and follow your plant procedures and permit. If you suspect a toxic discharge, a safety hazard or a permit violation, notify your supervisor right away.

This guide also appears on ActivatedSludge.com, our consulting site. Results are for training and operator use; always follow your plant’s procedures.